This is a randomized, placebo-controlled crossover study of the relationship between plasma levels of haloperidol and the electrocardiographic QT interval in poor and extensive metabolizers of cytochrome P450-2D6. Each of 20 healthy adult subjects will receive haloperidol and placebo in two 96-hour dosing periods separated by a 3-day washout period, the relative order of the drug and placebo being randomized. Pharmacokinetic sampling and EKG recordings will be taken at 13 points during each period. The usual PK parameters will be determined for each genotype. Fridericia-corrected QT intervals will be tested for dose-dependent prolongation.